1. Field of the Invention
The present invention relates to a portable apparatus, a system and a method for applying microwave energy directly to a medium in-situ without confining the medium. The apparatus, system and method are well suited for various environmental applications, such as in-situ remediation of soil, sludge or spills.
2. Description of the Prior Art
In applicant's previous patent, U.S. Pat. No. 4,853,507, an apparatus for separating emulsions is disclosed. In this apparatus, emulsions are irradiated with microwave energy through a confining applicator disposed within a wave-guide section, and rapidly heated emulsion is extracted for separation. By contrast, in the present invention, an applicator element of tapered geometry is applied directly to the medium to be heated, without confining the medium. The direct application of microwave energy allows for efficient dielectric heating of large masses of a medium, thus permitting in-situ remediation of large areas of contaminated soil or uncontained chemical spills.
In U.S. Pat. No. 4,067,683, now Reissue Pat. No. 32,241, an applicator element of tapered geometry connected directly to a microwave energy source is disclosed. In this patent, electromagnetic energy is directed toward a confined hydrocarbon fluid, where a metal tank enclosing the applicator element creates a cavity for resonant-type heating, as opposed to application of broad bandwidth radiation as in the present invention. Such a configuration requires that the medium to be heated flows through a holding tank, thus making the configuration unsuitable for use in in-situ remediation of a contaminated area. Reissue Pat. No. 32,241 also discloses, in a further embodiment, directing microwave energy downhole for interaction in a geological substrate. However, for this embodiment, the applicator element must be inserted into a hollow conduit and does not directly contact the medium to be heated.
In U.S. Pat. No. 5,076,727, a system is disclosed for the in-situ de-contamination of spills and landfills by use of focussed microwave/radio frequency (MW/RF) heating in combination with a closed loop vapor flushing and vacuum recovery system. However, the system described in this patent relies on either an above-ground horizontal array of energy sources, which uses induction (or eddy current) principles, or in-situ vertical electrodes. As described, the system refers only to resonant type heating and not the application of broad bandwidth radiation. Such a system exemplifies RF (1 MHz-300 MHz) heating only and makes no attempt to show a practicable embodiment of how to implement radiation in the microwave range (300 MHz and up).